The present invention relates to a transfer mechanism for successively transferring articles in one direction and, more particularly, to a transfer mechanism suitable for use in articles in a machine having a plurality of molds arranged in series, the articles or blanks from a receiving position to the mold of the first step and then to a mold of a second step.
A typical known transfer mechanism conventionally used for this purpose includes a pair of substantially parallel feed bars, a plurality of clamping jaws provided on the opposing surfaces of the feed bars, means for supporting the bars for movement in three orthogonal directions, and three independent drives operable in timed relation to effect cyclic movement of the bars in the three directions successively. In operation, two feed bars are moved toward each other to each pair of opposing clamping jaws clamp therebetween one blank. The bars are then moved upwardly so that the plurality of blanks clamped between pairs of clamping jaws are lifted simultaneously. Then, the bars are moved ahead by a predetermined distance and, after being lowered to a predetermined level, are moved away from each other to release all the blanks. The bars are finally moved back to resume the initial position.
In this conventional transfer mechanism, each drive comprise a drive shaft device including a shaft driven by the driving power source of the press or by an independent electric motor and a plurality of cams and gears mounted on the shaft, a plurality of levers, links and transmission shafts adapted to operate following up the motion of the drive shaft device, and a plurality of pneumatic cylinders adatped for bringing the levers into engagement with the cams.
In this conventional mechanism, the feed bars are operated at speeds determined by the contours of cams. It is, therefore, possible to obtain a very smooth movement of the feed bars without suffering any substantial impact and vibration. In consequence, various transfer failures such as incorrect clamping of the blank by the jaws, dropping of the same during forward movement and so forth are avoided.
This conventional mechanism, however, has the following drawbacks. Firstly, since the levers, links and other sliding members adapted to be operated by the cams are required to have sufficiently high rigidity, the weights of these parts is increased to impose a practical limit in increasing the speed of operation of the transfer mechanism. Secondly, it is to be pointed out that this conventional mechanism of a pure mechanical driving type has an impractically complicated construction, requiring much labor and time in maintenance and resulting in a high cost of production.
In order to obviate the above-explained drawbacks of the mechanical drive, it has been proposed by the inventors herein to actuate the feed bars hydraulically. In such hydraulic drive systems, however, the supply and discharge of the hydraulic oil to and from the hydraulic cylinders for driving the feed bars are controlled by means of a selector valve adapted to switch the direction of flow of the oil coming from a hydraulic pump. Therefoere, the movement of the feed bars in each direction is made at a constant speed from the start to the finish of each motion and the motions are performed in a discontinous manner by the switching of valves in accordance with limit signals. Impacts and vibrations thus inevitably take place in the operation of the transfer mechanism. To avoid the generation of impacts and vibrations, it is necessary to delicately control the opening of the valves during a very short period of time. Such control, however, is quite difficult to achieve from a technical point of view and requires a highly complicated and expensive control device solely for this purpose.